1. Field of the Invention
The present invention relates to the field of compressed air and gas systems, and more particularly to filtering and drying equipment for filtering and removing moisture from compressed air and gas delivered to air/gas-driven tools.
2. Description of Prior Art
Typical compressed air or gas produced by a compressor apparatus is saturated with 50% to 100% relative humidity, and also contains contaminants such as dirt, dust, oil, line debris and other matter. Filters and traps remove liquid water and other contaminants but do nothing to eliminate the 50% to 100% moisture vapor introduced by compressors, air lines, fittings, regulators and other equipment. This can cause problems in applications such as paint booth operations where compressed air or gas is used as a propellant to atomize and expel paint from a paint gun. If moisture-laden ambient air is delivered through the air/gas line, it will feed through the paint gun, and may cause unwanted fouling that results in a bad and unacceptable paint job.
The removal of this moisture vapor requires that an air/gas dryer system be used, such as a refrigerated dryer or an adsorbent type of dryer. Such systems are generally very effective, the latter being typically capable of drying compressed air or gas to below-zero dew point levels. There are several types of adsorbent dryers available for different applications. Large centralized adsorbent dryers are used in factories and other environments where compressed air/gas must be delivered to multiple points-of-use, such as a group of assembly line workers operating air tools. Such dryers are large complicated devices that are intended to be serviced by experienced technicians, as when the adsorbent therein is spent and needs to be replaced. At the other end of the spectrum, disposable point-of-use adsorbent dryers are available that can be connected between the end of an air/gas line and an air/gas tool (such as a paint gun). These simple devices are intended to be disposed of after a relatively small number of applications (e.g., painting several cars), when the modest amount of adsorbent material therein will usually be spent. Occupying a middle ground of the adsorbent dryer spectrum are various near point-of-use dryers adapted for in-line placement within approximately 10-20 feet (or less) of a point-of-use. For example, a commercial paint booth will often have a small adsorbent dryer mounted on the wall of the booth. These systems typically comprise adsorbent-containing canisters in which are disposed a quantity of desiccant or other adsorbent, or a removable cartridge containing such material. The inlet side of the canister receives moist air/gas from a compressed air/gas source while the canister's outlet side delivers dry air/gas to a short air/gas hose that the user connects to a point-of-use tool. In most such systems, the canister is a generally hollow cylinder that is approximately one foot in height and approximately six inches in diameter. Other sizes are also available, depending on drying capacity requirements.
A disadvantage of the above-described near point-of-use adsorbent dryer systems is that the removal and replacement of adsorbent requires disassembly of the canister or cartridge and the removal of the loose granular adsorbent therefrom for recycling, followed by the reintroduction of fresh adsorbent. This procedure can be messy, time consuming, and wasteful of adsorbent insofar as it is almost always the case that some of the adsorbent will spill out, scatter and become lost during the removal and recharging process. If a cartridge is involved, it needs to be disconnected from cartridge carrying components within the dryer and then reconnected thereto following recharging. As a result, personnel who use compressed air/gas tools typically do not want to be bothered with the task of replenishing these systems with new adsorbent when the old material is spent, and thus may continue to use them even after their moisture vapor removal capabilities are no longer optimal. Such personnel may adopt a “let the next guy do it” attitude when in comes to properly servicing and maintaining these systems.
A further consideration that must be taken into account when using a near point-of-use adsorbent drying system is the need to employ adequate means to ensure that any water'slugs in the compressed air/gas are separated and drained off before reaching the adsorbent. Contaminants such as compressor debris, oil, dirt, and the like also need to be filtered, typically down to approximately 0.1 micron or below. In conventional near point-of-use adsorbent dryer systems, separate coalescer and filter canisters are typically placed next to the adsorbent-containing canister to perform these functions. Each of these will have its own filter element that must be periodically removed and replaced. There also needs to be a means to filter out adsorbent “dust” before the dried air/gas is exited from the dryer for use in an application. Conventional near point-of-use adsorbent dryers provide an additional filter for this purpose, and this filter must also be periodically serviced.
It is to solving the foregoing problems that the present invention is directed. What is needed is an improved air/gas dryer for near point-of-use operation that is easy to install and use, and simple to maintain. The dryer should be suitable for use as the primary or sole air/gas moisture vapor treatment apparatus in a compressed air/gas system that serves a small number of users. The system should be capable of reducing moisture vapor content in a compressed air/gas stream down to a relative humidity of less than ½% (−40 degrees F. dew point). This means the no moisture will condense into liquid water until the compressed air/gas sees a temperature of −40 degrees F. below zero. Adding filtering and coalescing functions to such a dryer would be further desirable. It would be further desirable for such a system to have a ‘visual’ indication identifying the exact state of dryness. Constructing the system to be portable would be an additional advantageous feature.